Peak IC Research Articles

Electrochemical behavior of intramolecular cyclization reaction of catecholamines at carbon nanotube/carboxymethylcellulose electrode

• Intramolecular cyclization reaction of catecholamines is conducted. • A electron transfer-chemical reaction-electron transfer (ECE) process is addressed. • A carbon nanotube (CNT)/carboxymethylcellulose (CMC) electrode is used. • The electrochemical behavior in the ECE mechanism is justified by DigiElch simulation. • This work contributes to the in-depth understanding of catecholamines. Neurotransmitter catecholamines [dopamine (DA), epinephrine (EP), norepinephrine (NE), and 3,4-dihydroxyphenylalanine (DOPA)] exhibit an electron transfer-chemical reaction-electron transfer (ECE) reaction, wherein two electron transfer reactions are connected by a chemical reaction. The electrochemical behavior of catecholamines depends strongly on the kinetic property of the chemical reaction, that is, the intramolecular cyclization rate. This work provides systematic knowledge of the intramolecular cyclization reactions of catecholamines in the ECE process. We adopt a carbon nanotube (CNT)/carboxymethylcellulose (CMC) electrode because it shows an apparent ECE profile in cyclic voltammetry (CV) results, unlike other electrodes. The analysis of the electrochemical behavior in the ECE mechanism is justified by simulations using the DigiElch simulation program. The cyclization rate of various catecholamines follows a specific order: DA < NE < DOPA < EP. Because the cyclization step involves hydrogen ions, the rate depends on pH—the cyclization rate increases with a decrease in pH. The electrochemical behavior due to cyclization is verified on the basis of the CV results, particularly the change in the intensity of the cathodic peak (Peak Ic) due to the reduction of catecholamine- o -quinone. The intensity of Peak Ic is determined by (i) the type of catecholamines, (ii) pH, and (iii) the time scale of CV. This work contributes to the in-depth understanding of catecholamines and the development of novel strategies for the electrochemical sensing of catecholamines.

Boosting the Rate Performance of Li–S Batteries via Highly Dispersed Cobalt Nanoparticles Embedded into Nitrogen-Doped Hierarchical Porous Carbon

Boosting the Rate Performance of Li–S Batteries via Highly Dispersed Cobalt Nanoparticles Embedded into Nitrogen-Doped Hierarchical Porous Carbon

Technical Note: Design and characterization of a large diameter parallel plate ionization chamber for accurate integral depth dose measurements with proton beams.

The goal was to develop and test a large diameter parallel plate ionization chamber capable of intercepting at least 98% of the proton beamlets tested with the system. A commercial synchrotron proton therapy system was used for the study (Hitachi, Ltd, Hitachi City, Japan; Model: Probeat-V). The energies investigated were in the range of 100 to 192MeV. Three beam spot options available from the system were used. A PTW Bragg peak IC of diameter 84mm (BP84) (Model PTW34070) was employed for comparison in a scanning water phantom. A prototype of 150mm diameter was produced (PTW, Freiburg, Germany; model: T34089) and used for the testing. Monte Carlo calculations were also performed with FLUKA to guide the BP150 design and for comparison to the radiological measurements. For comparison, a 40cm diameter ideal virtual detector was included in the Monte Carlo model. The measured proton range R90 agrees between the BP84 and BP150 ionization chambers within +0.06/-0.27mm across the energies 100-192MeV, which is less than the daily experimental setup uncertainty of 0.4mm. The differences in the absolute integral depth dose curves (IDDs) between the BP84 and BP150 ranged from 0.3% to 1.0% for the spot sizes and beam energies tested. As predicted by the Monte Carlo modeling, the greatest differences were found in the plateau region of the IDDs. Also, the IDDs measured with the BP150 were very similar to those of the ideal 40cm diameter detector Monte Carlo simulations. We conclude that the BP150 offers a small, but a useful reduction in uncertainty from the nuclear halo effect for the system under test.

Mechanical Strength Evaluation of the Internal Matrix Reinforced Nb3Sn Multifilamentary Wires Using Cu–Sn–In Ternary Alloy Matrix

We investigated the simple internal reinforcement method using special reinforcement ternary bronze alloy matrix on the bronze processed Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wire. The Cu-Sn-Zn ternary alloy matrix was transformed to the (Cu, Zn) solid solution after Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn synthesis based on the solid solution strengthening mechanism. For the further mechanical strength improvement, we focused on the Indium (In) as the more effective solute element for the “internal matrix strengthening”, and succeeded to fabricate the bronze processed Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn multifilamentary wire using various Cu-Sn-In-(Ti) ternary alloy matrices. Changes of the Vickers hardness before and after Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn synthesis and the transport critical current (Ic) under the uniaxial tensile deformation were evaluated. Vickers hardness of the matrix after Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn synthesis on the Cu-Sn-In ternary alloy matrix samples was higher compared with the conventional bronze and the Cu-Sn-Zn ternary matrix samples. On the other hand, the tensile stress obtained to the maximum peak Ic value on the Cu-Sn-In ternary alloy matrix sample was estimated to approximately 265 MPa, and this value was much higher than those of the Cu-Sn-Zn ternary matrix and conventional bronze processed samples. We found that the In element would become more attractive solute element than Zn element for the internal reinforcement ternary matrix.

Impact of Lateral Scaling on Silicon Germanium High Breakdown Power Amplifier Device Performance

Silicon Germanium (SiGe) Heterojunction Bipolar Transistors (HBTs) in Bipolar Complementary Metal Oxide Semiconductor (BiCMOS) technologies have in recent years, emerged as a viable alternative to Gallium Arsenide (GaAs) [1] for commercial development of linear power amplifier (PA) modules for wireless communications. The explosion in WLAN applications at 2.4GHz has provided ample opportunity for SiGe BiCMOS to substantially penetrate the PA market [2]. SiGe HBTs offer several benefits compared to it’s GaAs HBT counterparts including the ability to provide high integration at a reduced cost [3]. The higher thermal conductivity associated with the silicon substrate enables reduced chip areas, smaller packages and provides improvements in chip robustness. Additionally, SiGe BiCMOS integration facilitates improved power densities, on-chip matching and bias chokes, temperature compensated power detector and a CMOS compatible interface [2]. SiGe HBT PA device design limits have traditionally been constrained by the performance tradeoff described by the Johnson limit, which states that the product of the current gain, fT and the DC open-base breakdown voltage, BVceo, should be relatively constant[3]. However, it is now generally accepted that DC emitter-open breakdown voltage, BVcbo is a more useful indicator of device ruggedness for PA applications. This arises since SiGe HBT operation in PA applications have been demonstrated at voltages significantly higher than BVceo, [1,4]. Furthermore, power-gain cut-off frequency, fMAX , has also been cited as relevant a device metric for PAs as fT , [1,3] and several authors have suggested that improvements in fMAX will enhance PA device performance. Typically, improvements in device fMAX are achieved by lateral scaling to accomplish a reduction in the base resistance and collector-base capacitance. Since SiGe HBT device physics do not demand rigid tradeoff between BVcbo and fMAX, , several potential device optimization opportunities exist for PA applications. Technology computer-aided design (TCAD) has been used to optimize the PA design performance relative to the base technology. The TCAD methodology was based on a detailed strategy which entailed developing a process and device model calibration for an existing 0.35um SiGe HBT device that features non-self-aligned emitter-base integration, with a carbon doped SiGe base layer and an implanted extrinsic base region [2]. The model calibration featured a close match of both process and electrical characteristics to the measured data. An important element to matching the electrical characteristics of the device, was simulating key artifacts of the process related to epitaxial growth of the SiGe base layer, which defined the final device topology. The calibration served as the baseline simulation for the optimization study and provided insight into the device performance limitations. The simulations demonstrated the device breakdown, BVcbo, occurs along the extrinsic region of the collector and the base, and is correspondingly set by the thickness of the collector n-epitaxial layer and the vertical diffusion of the extrinsic base into the collector. Several lateral scaling strategies were therefore investigated, which addressed optimization of collector-base capacitance, Ccb and base resistance, Rb for improvements in fMAX and BVcbo. Scaling the lateral dimension of the device resulted in improvements in the performance metrics peak fT , peak Ic and fMAX . Improvements in fT and Ic are explained by the reduced surface field effect, whereby a more uniform field distribution delays base push out effect in the transistor[5]. The AC and DC characteristcs will be reviewed.

Metal toxicity in the spotted dogfish Scyliorhinus canicula

In most vertebrate groups high levels of urea in the plasma are not tolerated. However, elasmobranchs have adapted a variety of mechanisms to counteract the potential harmful effects of the high concentration of urea (>300 mM) in their plasma. One such method is the retention of methylamines that counteract the toxicity of urea, the most notable of which is trimethylamine oxide (TMAO). A customary method for measurement of TMAO involves the reduction of TMAO to TMA followed by the extraction and analysis of the amine in its picrate form (Wekell and Barnett, 1991). In the alternative method TMAO was measured by ion exchange chromatography (Metrhom Peak). Briefly, plasma samples from the little skate, Raja erinacea, (10 ml) were diluted with 10 ml of MilliQ water and injected onto a cation exchange column (Metrosep 2-150) using a mobile phase of 4 mM tartaric acid and 0.75 mM dipicolinic acid at a flow rate of 1 ml min−1. Cation detection was achieved using a Metrohm Peak IC 819 detector. TMAO was measured in the same samples using the method first described by Wekell and Barnett (1991) and results were found to be comparable. Additional methylamines and b-amino acids did not interfere with the measurement of TMAO and under these conditions TMAO did not interfere with the measurement of other ions from the same sample. This method was advantageous because; much less sample was required for measurement; there was no requirement for strong solvents; and multiple cations were measured from the same sample. Wekell and Barnett (1991), J. Food Sci. 56, 132–135. Email Address for correspondence: andersow@cc.umanitoba.ca

Interaction of Antiprotozooal Drugs with Biomolecules. An ESR and UV-Vis Spectroelectrochemical Study.

Cyclic voltammetric study in aprotic medium of antiprotozooal nitro compounds, Nifurtimox, Benznidazol and Niclosamide in the presence of glutathione and triolein, compounds that mimic the cellular constituents of the living being, were carried out in order to investigate the interactions of these compounds with the electrogenerated intermediaries in the reduction of the nitro compounds. Glutathione caused an important shift potential of the dianion radical (peak IIc) of nifurtimox and benznidazol and a minimum interaction with the radical anions (peak Ic). However, a significant change in the voltammetric behavior of nifurtimox was observed for both peaks Ic and IIc with triolein. Niclosamide presented more complicated responses. ESR experiments with nifurtimox showed that the nitro radical anion is interacting with triolein, even at very small concentrations.

Voltammetric and amperometric studies of thiocholine at a screen-printed carbon electrode chemically modified with cobalt phthalocyanine: studies towards a pesticide sensor

Cyclic voltammetry was used to investigate the electrochemical behaviour of thiocholine at screen-printed carbon electrodes chemically modified with cobalt phthalocyanine. Cyclic voltammograms exhibited one anodic peak (Ia) and two cathodic peaks (Ic and IIc) in the potential range –0.8–+0.3 V between pH 5.0 and 12.0. Peak Ia is considered to result from the electrocatalytic oxidation of the thiol moiety to produce the corresponding disulfide; peak Ic is likely to be the electrocatalytic reduction of the disulfide back to the original thiol species. Peak IIc is probably due to a reduction process occurring in the macrocyclic phthalocyanine molecule. Hydrodynamic voltammetry was performed in 0.05 mol dm–3 phosphate buffer (pH 8.0) containing thiocholine; one well-defined anodic wave was obtained. From this, the optimum potential for amperometric studies was found to be +0.1 V. Calibration studies were performed using amperometry in stirred solution; a linear response was obtained over the range 5.0 × 10–7–4.8 × 10–5 mol dm–3. It should be possible to use these screen-printed electrodes as the basis of a pesticide sensor.

銅‐ニオブ補強安定化Ｎｂ３Ｓｎ複合多芯超伝導線材のひずみ特性

Bronze processed multifilamentary Nb3Sn superconducting wires with the reinforcing stabilizer CuNb in stead of the conventional Cu stabilizer were fabricated. The mechanical properties and the strain dependence of the critical current, Ic, were evaluated at 4.2K and a magnetic field of 15T. A remarkable increase in the yield stress of 70% and the plastic flow stress as compared with those in the wire with Cu stabilizer were observed. The strain for the peak Ic was also increased by 0.2%. Ic on unloading was reversible within the strain range of 1.5%. The strain sensitivity of Ic in the Cu-Nb/Nb3Sn wire was almost the same as that of the Cu/Nb3Sn wire. Decrease in the wire diameter from 0.8 to 0.5mm resulted in a slight increase in the flow stress of the CuNb/Nb3Sn wire, but no change in the strain dependence of Ic. The heat treatment temperature rise from 700 to 750°C resulted in a decrease in the yield stress of 15%, but no change in the strain dependence of Ic. Marked change in morphology of Nb filament in the CuNb reinforcing stabilizer during the heat treatment was evidenced.

Carbon incorporation in ZnSe grown by metalorganic chemical vapor deposition

Carbon incorporation in ZnSe films grown by metalorganic chemical vapor deposition is reported. Secondary-ion mass spectrometry measurements in ZnSe films grown from methylallylselenide and dimethylzinc show an enhanced carbon accumulation at the interface between ZnSe and GaAs. The carbon incorporation in the bulk ZnSe increases with the VI/II ratio and for a value of VI/II=3–4, the amount of incorporated carbon abruptly jumps to concentrations of 1021 cm−3, whereupon the films become polycrystalline. A new shallow peak IC at 2.7920 eV dominates the near-band-edge low-temperature photoluminescence spectra of all carbon-contaminated ZnSe films. The intensity and linewidth of IC increase with the VI/II ratio in a similar manner to the carbon concentration. This peak is proposed to be due to the radiative decay of excitons bound to a complex defect, which is associated with the presence of carbon in the films.

実用Ｎｂ３Ｓｎ超電導線材の構成と臨界電流のひずみ依存性

An investigation was made on the strain dependence of critical cuurent Ic for three kinds of practical Nb3Sn superconducting wires which are in the course of development, with an emphasis on the correlation with wire constitution.In the internal tin diffusion processed wires with a single tin core at the center, the reversible strain limit, εirrev was small and the strain sensitivity of Ic was high. This is ascribed to the strain concentration induced by Kirkendall voids observed in the center of fracture surface.Internal reinforcement using SUS 405 steel increased both εm, the strain corresponding to peak Ic, and the strain sensitivity, and decreased the εirrev in addition to a marked increase of flow stress. In the light of both the serration in the stress-strain relation and fracture surface morphology, the degradation of strain characteristics are attributable to the strain concentration in Nb3Sn layer associated with localized deformation of the steel at low temperatures.In the external tin diffusion in situ processed wires, both Nb3Sn layer formed in the periphery and the unreacted core in the center of the wire controlled the strain characteristics. The smaller the core size was, the larger the critical current density and the smaller the εm or εirrev. Inhomogeneity of tin diffusion in the cross section as well as in the longitudinal direction resulted in deviation of the core and tin balling, respectively. They deteriorated the strain characteristics of the wire significantly.Improvements of the strain characteristics in these wires through proper constitution and heat treatment were briefly discussed.

Calcium activates and inactivates a photoreceptor soma potassium current

Light-induced currents were measured with a two-microelectrode voltage clamp of type B photoreceptor somata, which had been isolated by axotomy from all synaptic interactions as well as from all membranes capable of generating impulse activity. In artificial seawater (ASW), light elicited a transient early inward current, INa+, which depended on Na+o and had a linear current-voltage relation and an extrapolated reversal potential of 30-40 mV (absolute). In 0-Na+ ASW, light elicited a transient short-latency outward current that dependent on K+o, increased exponentially with more positive voltages (greater than or equal to -40 mV), and reversed at -70 to -75 mV. This outward current was not blocked by Ca++ channel blockers (e.g., Cd++, Co++) or substitution of Ba++o, for Ca++o, but was reduced by iontophoretic injection of EGTA. In both ASW and 0-Na+ ASW, light also elicited a delayed, apparently inward current, which was associated with a decreased conductance, depended on K+o, increased exponentially with more positive voltages (greater than or equal to -40 mV), reversed at the equilibrium potential for K+ flux in elevated K+o was eliminated by substitution of Ba++o for Ca++o, and was greatly reduced by Cd++o or Co++o. Thus, light elicited an early Ca++-dependent K+ current, IC, and a prolonged decrease of IC. Iontophoretic injection of Ca++ through a third microelectrode caused prolonged reduction of both IC and the light-induced decrease of IC, but did not alter ICa++ or the current-voltage relation of IC. Ruthenium red (1 microM) in the external medium caused a prolongation of the light-induced decrease of IC. Iontophoretic injection of EGTA often eliminated the light-induced IC decrease while decreasing peak IC (during depolarizing steps to -5 or 0 mV) by less than one-half. EGTA injection, on the average, did not affect steady state IC but reduced the light-induced decrease of steady state IC to approximately one-third of its original magnitude. The prolonged IC decrease, elicited by dim light in the absence of light-induced IC or INa+, was more completely eliminated by EGTA injection. It was concluded that light, in addition to inducing a transient inward Na+ current, causes both a transient increase and a prolonged decrease of IC via elevation of Ca++i.

Use of Primary Beam Filtration in Estimating Mass Attenuation Coefficients by Compton Scattering

AbstractMass attenuation coefficients (MACs) are frequently estimated over a range of wavelengths in x-ray spectrometry from the intensity of the Compton peak IC associated with a prominent tube line. The MAC μλ at wavelength λ is estimated from the MAC at the Compton wavelength λC with the approximations μλ α μC and μC α 1/IC. Systematic errors may introduce absorption edge bias (AEB) effects into the results, caused by sample components vith absorption edges between λc and λ. A procedure is described which eliminates AEB effects by measuring IC using emission radiation from a primary beam filter.